As such a transmission that comprises a continuously variable transmission, which transmits the rotational driving force of an engine to driving wheels with a speed change, there is known a transmission that incorporates a single pinion type planetary gear train as a forward/reverse switching mechanism, which is used for switching the driving direction of a vehicle (for example, refer to Japanese Laid-Open Patent Publication No. 2003-120721). For example, the sun gear of the planetary gear train receives the rotational driving force of the engine, and the ring gear is used as the output member for handing the rotational driving force successively to the continuously variable transmission. In the planetary gear train, a forward clutch is used for fixing the sun gear and the ring gear stationary, so that the rotational direction produced thereby corresponds to the forward direction of the vehicle. On the other hand, a reverse brake is used for fixing the carrier, so that the rotational direction produced by the gear train corresponds to the rearward direction of the vehicle.
While the transmission is set in the reverse range, the rotational speed at which the rotational driving force is input from the engine is reduced in the planetary gear train, and the driving force is output at this reduced speed to the continuously variable transmission. In other words, the continuously variable transmission receives an input torque that is much larger than that output by the engine. For restraining the thrust being applied onto the continuously variable transmission against this input torque, an upshifting is executed, and the ignition is retarded for eliminating any abrupt change in the torque until the upshifting is complete.